1. Field of the Invention
This invention relates to a roller leveler used for leveling the surface shape of a hoop passed through a rolling process.
2. Description of the Prior Art
A roller leveler basically comprises an upper work roll group and a lower work roll group both defining a pass line, through which a rolled hoop is passed. Both of the upper and lower work roll groups are provided in a zigzag form so that three points of intersection of three adjoining upper and lower work roll axes with the plane crossing them may form three vertexes of an isosceles triangle.
The hoop passing through the pass line is bent along the cylindrical surfaces of the respective work rolls and extended up to its plastic zone. As a result, the strain of the hoop surface is removed. That is, the surface shape of the hoop is leveled.
However, on the basis of the diameters of the work rolls of a roller leveler or the respective pitches between mutual upper work rolls and between mutual lower work rolls, the thickness of the hoop which can be processed by the roller leveler is determined. If the processable range of the hoop thickness is wider, the leveling of the hoop processed by using a plurality of roller levelers can be practiced by a single roller leveler.
In a prior art, there has been proposed a roller leveler (refer to Japanese Patent Disclosure (KOKAI) No. 62-203616), in which a pair of upper and lower work rolls adjacent to each other in a diagonal direction are made movable in an upper and lower direction to the other pair of upper and lower work rolls adjacent to these work rolls, respectively, and the lower work roll group is made movable in a lateral direction which is normal to its axis.
According to this roller leveler, after moving a pair of diagonal directional upper and lower work rolls in the upper and lower direction, respectively, the lower work roll group is moved in the lateral direction so that the moved upper and lower work rolls may mutually face to the respective other fixed lower and upper work rolls. As a result, both upper and lower work roll groups having their pitches which are twice as large as those prior to their moving are newly composed. A work roll arranged in a large pitch, in comparison with the work roll arranged in a pitch smaller than that work roll, makes it possible to level the hoop shape having a larger thickness, on the basis of the same pressure applied to the hoop.
Now, the upper and lower work roll groups defining a pass line must be accurately arranged and maintained so that these axes may pass through the vertexes of the isosceles triangle. This is indispensable for the leveling of a thin plate.
In the prior art roller leveler, however, there is a large possibility that any abrasions, rusts, dust or the like produced between laterally movable supporting means for supporting the lower work roll group and the other portions of the roller leveler may damage the accurate arrangement of the lower work roll group. Therefore, it is not desirable for maintaining the highly accurate roller leveler to make the lower work roll group movable in a lateral direction.